Fan rpm control method

ABSTRACT

Temperature of each cooling target fluid is detected. When the flow rate of a cooling target fluid passing through a cooling system is high, the fan revolution speed of a cooling fan of the cooling system is controlled to achieve a target fan revolution speed so that the detected temperature of the cooling target fluid reaches a preset target temperature. In cases where the engine is in a low idling state, the flow rate of each cooling target fluid passing through the cooling system is reduced. The fan revolution speed of the cooling fan is controlled to achieve a new target fan revolution speed that is lower than the target fan revolution speed.

TECHNICAL FIELD

The present invention relates to a fan revolution speed control methodfor controlling fan revolution speed of a cooling fan of a coolingsystem. The aforementioned revolution speed system a number ofrevolutions per unit period of time and is hereinafter referred tosimply as “revolution speed”.

BACKGROUND OF THE INVENTION

An engine for driving pumps is provided with a main pump and a fan pump.The main pump is for excavation or other work and serves to drive aworking unit system and a turning system of a hydraulic shovel. The fanpump serves to perform variable control of the pump discharge rate of afan pump by system of an electro-hydraulic transducing valve so as tocontrol the revolution speed of the fan motor that is adapted to drive acooling fan for cooling an intake air cooler, an oil cooler, and aradiator. Through the control of the revolution speed of the fan motor,the fan pump serves to control the fan revolution speed of the coolingfan. The electro-hydraulic transducing valve is controlled by acontroller. Temperature sensors respectively detect temperatures of theintake air, the hydraulic oil, and the coolant, all of which are cooledby the cooling fan. The controller serves to control the fan revolutionspeed of the cooling fan by controlling the flow rate of the hydraulicoil fed from the fan pump so that the detected temperatures are broughtto the same level as the respective target temperatures that have beenset beforehand (refer to Japanese Patent No. 3295650 as an example).

Japanese Patent No. 3295650 mentioned above describes an automaticengine speed control system (hereinafter referred to as “AEC”) forautomatically reducing the engine speed to a given, low revolution speedand a one-touch low idling switch to be operated by an operator with asingle operation so as to put the engine in the one-touch low idlingstate, in which the engine speed is controlled at a given, low speed.When the levers are at the neutral position, the hydraulic actuators areprevented from being operating. Should the engine be in either one ofthe aforementioned two states when the levers are at the neutralposition, i.e. the AEC state when AEC is on or the one-touch low idlingstate, the engine speed is lower than in cases where the working unit isin operation. Regardless of the reduction in the engine speed, however,there is virtually no decrease in the fan speed, because the controllercontrols the fan revolution speed of the cooling fan by controlling thepump discharge rate of the fan pump so as to bring the detectedtemperature of each cooling target fluid, such as the hydraulic oil, tothe same level as each respective target temperature determinedbeforehand. In other words, there is virtually no decrease in the amountof cooling air.

To summarize, the controller is adapted to control the fan revolutionspeed of the cooling fan by controlling the pump discharge rate of thefan pump so as to bring the detected temperature of each cooling targetfluid, such as the hydraulic oil, to the same level as each respectivetarget temperature determined beforehand. Therefore, when the detectedtemperature of a cooling target fluid, such as the hydraulic oil, ishigh, the controller controls the fan revolution speed of the coolingfan at a high speed.

Should the levers be returned to the neutral position during heavy loadoperation, the controller reduces the engine speed by system of eitherthe AEC control or the one-touch low idling control while controlling acapacity changing system, such as a swash plate, of the variabledelivery pump that serves to feed the hydraulic oil to the hydraulicactuators, thereby reducing the pump discharge rate of the variabledelivery pump. As a result, the flow rate of the hydraulic oil fed tothe hydraulic actuators is reduced sharply, resulting in sharp decreaseof the flow rate of the oil returned to the tank from the hydraulicactuators through the oil cooler.

This may cause thermal strain resulting from the hydraulic oil in theoil cooler being rapidly cooled by the cooling fan rotating at a highspeed to cope with the high temperature of the hydraulic oil. Suchthermal strain presents the possibility of breakage of or other damageto the oil cooler.

In order to solve the above problems, an object of the invention is toprovide a fan revolution control method that is capable of improving thedurability of a cooling system provided with a cooling fan by reducingthermal strain that occurs in such cooling system.

DISCLOSURE OF THE INVENTION

A fan revolution speed control method according to the present inventioncalls for detecting a temperature of a cooling target fluid andcontrolling the fan revolution speed of a cooling fan of a coolingsystem for cooling the cooling target fluid so that when the flow rateof the cooling target fluid passing through the cooling system is high,the fan revolution speed of the cooling fan is controlled to achieve atarget fan revolution speed in order to bring the detected temperatureto the same level as a preset target temperature, and that when the flowrate of the cooling target fluid becomes lower, the fan revolution speedof the cooling fan is controlled to achieve a new target fan revolutionspeed that is lower than the target fan revolution speed. Should theflow rate of a cooling target fluid or fluids passing through thecontrol system be reduced, the fan revolution speed of the cooling fanis controlled to achieve the new target fan revolution speed, which islower than the target fan revolution speed. As this prevents rapidcooling of the cooling target fluid(s) flowing in the cooling system ata reduced flow rate and thereby suppress occurrence of thermal strain inthe cooling system, the durability of the cooling system is improved.

A fan revolution speed control method according to another feature ofthe invention calls for detecting a temperature of hydraulic oil in ahydraulic circuit and controlling the fan revolution speed of a coolingfan of an oil cooler that serves to cool the return oil from a hydraulicactuator so that when a lever for feeding hydraulic oil to the hydraulicactuator is being operated, the fan revolution speed of the cooling fanis controlled to achieve a target fan revolution speed in order to bringthe detected temperature to the same level as a preset targettemperature, and that when the lever is at a neutral position, duringwhich period supply of the hydraulic oil to the hydraulic actuator is atstandstill, the fan revolution speed of the cooling fan is brought to anew target fan revolution speed that is lower than the target fanrevolution speed. As described above, the new target fan revolutionspeed for the period during which the lever is at the neutral positionis lower. Therefore, even when the hydraulic oil is flowing in the oilcooler at a reduced flow rate as a result of operating the lever to theneutral position, the method described above is capable of preventingrapid cooling of the hydraulic oil in the oil cooler and suppressingoccurrence of thermal strain in the oil cooler, resulting in theimproved durability of the oil cooler.

A fan revolution speed control method according to yet another featureof the invention is similar to the fan revolution speed control methoddescribed above and further characterized in that when reducing theengine speed of a pump driving engine in the hydraulic circuit for theperiod during which the lever is at the neutral position to a levellower than that for the period during which the lever is being operated,the new target fan revolution speed for the period during which thelever is at the neutral position is calculated by multiplying the fanrevolution speed at that time by the ratio of the engine speed for theperiod during which the lever is at the neutral position to the enginespeed for the period during which the lever is being operated.Therefore, when the lever is at the neutral position, the new target fanrevolution speed for the period with the lever at the neutral positionis calculated by reducing the target fan revolution speed to achieve theratio of the engine speed when the lever is at the neutral position tothe engine speed when to the lever is operated. As a result, the fanrevolution speed can be reduced to the optimal level without the problemof excessive reduction of the fan revolution speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing a fan revolution control method accordingto an embodiment of the present invention;

FIG. 2 is a block diagram of a control device for employing theaforementioned control method;

FIG. 3 is a block diagram showing an algorithm for the control method;

FIG. 4 is a block diagram showing the structure of a PI control unit forthe control method;

FIG. 5 is a side view of a hydraulic excavator; and

FIG. 6 is a perspective of the interior of a cab of the aforementionedhydraulic excavator.

PREFERRED EMBODIMENT OF THE INVENTION

Next, an embodiment of the present invention is explained hereunder,referring to FIGS. 1 through 6.

FIG. 5 shows a hydraulic excavator as a work machine or a constructionmachine, which comprises an undercarriage 1 and an upper structure 2rotatably mounted on the undercarriage 1. The upper structure 2 isprovided with a power unit 3, a control valve unit (not shown), a cab 4,a working unit 5, and other necessary components. The power unit 3 ismainly comprised of a pump driving engine and hydraulic pumps driven bythis engine. The control valve unit serves to control a hydrauliccircuit. The hydraulic pumps serve as the pressurized oil source of theaforementioned hydraulic circuit. The cab 4 covers the space in which anoperator performs operations.

A boom 5 bm is provided and adapted to be swung by boom hydrauliccylinders 5 bmc. An arm 5 am is secured to the distal end of the boom 5bm by a shaft and adapted to be swung by an arm hydraulic cylinder 5amc. A bucket 5 bk is secured to the distal end of the arm 5 am by ashaft and adapted to be swung by a bucket hydraulic cylinder 5 bkcthrough a bucket linkage 5 bl. These components constitute theaforementioned working unit 5. The hydraulic cylinders mentioned aboveserve as hydraulic actuators.

FIG. 6 shows the interior of the aforementioned cab 4. Operation levers7L,7R for performing excavation or other works are provided at bothlateral sides of an operator's seat 6. A one-touch low idling switch 8is provided on the upper end of one of the operation levers, i.e. theoperation lever 7R, to enable the reduction of the revolution speed ofthe pump driving engine to a low-idling state by system of a singleoperation by the operator. A monitor 9 serving as a display deviceequipped with input capability is installed at the forward part of thecab interior.

FIG. 2 shows an outline of a fan revolution speed control device. Thepump driving engine (hereinafter simply referred to as “engine”) 11 ismounted on the motor vehicle of a construction machine, such as ahydraulic excavator. The engine 11 is provided with a main pump 12 forexcavation or other work and a fan pump 13 and has a function of drivingthese pumps 12 and 13 together. The main pump 12 serves to feedhydraulic oil under pressure.

The main pump 12 serves to feed hydraulic fluid, i.e. hydraulic oil, tovarious hydraulic actuators, including hydraulic motors of the travelingsystem, a hydraulic rotating motor 5 sw for rotating the upper structure2, and the hydraulic cylinders of the working unit, such as the boomhydraulic cylinders 5 bmc, the arm hydraulic cylinder 5 amc, and thebucket hydraulic cylinder 5 bkc.

The fan pump 13 serves to drive a fan motor 15 by system of hydraulicfluid that is hydraulic oil discharged into a pipe line 14. The fanmotor 15 is provided with a cooling fan 17, which is integrally attachedto a rotary shaft 16 of the fan motor 15 so as to be rotated by the fanmotor 15.

The fan pump 13 is provided with an electro-hydraulic transducing valve18, which is adapted to receive electrical input signals and outputhydraulic signals, so that the fan pump 13 functions as a variabledelivery pump to perform variable control of the rotation speed of thefan motor 15 by changing the pump discharge rate of the fan pump 13based on hydraulic signals output from the electro-hydraulic transducingvalve 18.

The main pump 12 is provided with an electro-hydraulic transducing valve19, which is adapted to receive electrical input signals and outputhydraulic signals, so that the main pump 12 functions as a variabledelivery pump to perform, based on hydraulic signals output from theelectro-hydraulic transducing valve 19, variable control of the pumpdischarge rate of the hydraulic oil fed from the main pump 12 to acontrol valve 20.

The control valve 20 has a plurality of spools adapted to bepilot-operated by system of pressurized pilot oil fed from pilot valves7L1-7L4,7R1-7R4, which are adapted to be the operation levers 7L,7R orfoot pedals (not shown). The control valve 20 serves to control thedirection and flow rate of the hydraulic oil that is fed from the mainpump 12 through the aforementioned spools to the hydraulic actuators.

The cooling fan 17 is a part of a cooling system 30. In addition to thecooling fan 17, the cooling system 30 includes an intake air cooler 21,an oil cooler 22, and a radiator 23, which are sequentially disposedopposite and share the cooling fan 17. The intake air cooler 21, the oilcooler 22, and the radiator 23 are respectively provided with an intakeair pipeline 24, a hydraulic oil pipeline 25, and a coolant pipeline 26.

The hydraulic oil pipeline 25 is a pipeline for returning the hydraulicoil from the hydraulic actuators through the control valve 20 into atank. The oil cooler 22 serves to cool the return oil flowing in thehydraulic oil pipeline 25.

The intake air pipeline 24 is provided with an intake air temperaturesensor 27 for detecting a temperature of the intake air, which is acooling target fluid. The hydraulic oil pipeline 25 is provided with ahydraulic oil temperature sensor 28 for detecting a temperature of thehydraulic oil, which is another cooling target fluid. The coolantpipeline 26 is provided with a coolant temperature sensor 29 fordetecting a temperature of the coolant (cooling water), which is yetanother cooling target fluid. These temperature sensors 27,28,29 areconnected to a signal input part of a controller 34 through respectiveinput signal lines 31,32,33.

A signal output part of the controller 34 is connected to a signal inputpart of each electro-hydraulic transducing valve 18,19 mentioned abovethrough each respective operation signal line 35 a,35 b.

The engine 11 is provided with an axle actuator 11 a. Signals processedby the controller 34 are output as operation signals through a signalline 35 c into the axle actuator 11 a. The actual amount of operatingperformed by the axle actuator 11 a is detected by a position sensor 11b. An engine revolution speed is detected by a revolution speed sensor11 c. These detected values are fed back to the controller 34, throughsignal lines 35 d,35 e respectively.

Other components connected to the controller 34, which serves to controlthe revolution speed of the engine 11 (hereinafter referred to as“engine speed”), mainly comprise the aforementioned one-touch low idlingswitch 8, an AEC switch 36 aec, an axle dial 36 acc, and lever operationdetecting switches 36 lev. The one-touch low idling switch 8 serves toactivate the one-touch low idling system for reducing the engine speedto a low-idling state by system of a single operation by the operator.The AEC switch 36 aec serves to activate an automatic engine speedcontrol system (hereinafter referred to as “AEC”) for automaticallyreducing the engine speed to a given, low revolution speed when thelevers are at the neutral position. Each lever operation detectingswitch 36 lev serves to detect whether the corresponding operation lever7L,7R is at the neutral position or an operative position. Each leveroperation detecting switch 36 lev performs this detection directly orindirectly through changes in pressure in the hydraulic circuit.

AEC is a system intended to automatically reduce the engine speed inorder to save the fuel and reduce noises and vibrations when theoperation levers 7L,7R are at the neutral position. There are two levelsof AEC: a first-stage AEC and a second-stage AEC, which can be changedover by system of the AEC switch 36 aec on a switch panel. For example,at the first-stage AEC, the engine speed may be reduced from a no-loadspeed by 100 rpm. At second-stage AEC, the engine speed may be reducedto a desired speed, e.g. 1300 rpm.

Should at least one of the operation levers 7L,7R be operated when AECis on, the engine speed is automatically returned to a given revolutionspeed that has been set by the use of the axle dial 36 acc beforehand.

The aforementioned one-touch low idling system is a system intended toreduce the engine speed to a given, low revolution speed, e.g. 1100 rpm,in order to save the fuel and reduce noises and vibrations in accordancewith the intention of the operator. In other words, this system isactivated by system of, for example, pushing the one-touch low idlingswitch 8 on the top of the right lever 7R when the operation levers7L,7R are at the neutral position.

Should the one-touch low idling switch 8 be pushed again or either oneor both of the operation levers 7L,7R be operated in the course of theone-touch low idling, the engine speed is returned to the previous speedthat has been set by the axle dial 36 acc.

The controller 34 is adapted to process signals representing thetemperature data detected by the temperature sensors 27,28,29 and outputsignals for the electro-hydraulic transducing valve 18 to change thepump discharge rate of the fan pump 13 based on the signals output fromthe controller 34, thereby controlling the fan revolution speed of thecooling fan 17 in order to bring detected temperatures of the coolingtarget fluids, such as the intake air, the hydraulic oil, and thecoolant, which are respectively detected by the temperature sensors27,28,29, down to the same level as the predetermined respective targettemperatures. The controller 34 thus cools the cooling target fluidsappropriately to prevent overheating.

As shown in FIG. 3, the controller 34 has an algorithm to performvariable control of the fan revolution speed based on detectedtemperatures of the respective cooling target fluids.

Referring to FIG. 3, signals that represent various temperatures, i.e. apredetermined intake air target temperature Tti, a detected intake airtemperature Tmi detected by the intake air temperature sensor 27, apredetermined hydraulic oil target temperature Tto, a detected hydraulicoil temperature Tmo detected by the hydraulic oil temperature sensor 28,a predetermined coolant target temperature Ttc, and a detected coolanttemperature Tmc detected by the coolant temperature sensor 29, are inputinto their corresponding proportional integral control units, which arerespectively provided for the different types of cooling target fluids.In the explanation hereunder, these proportional integral control unitsare referred to as PI control units 37,38,39.

The PI control units 37,38,39 serve to determine a plurality of targetfan revolution speeds respectively for the various cooling targetfluids, i.e. the intake air, the hydraulic oil, and the coolant, basedon the calorific value and the ambient temperature of each respectivecooling target fluid. Signals representing a target fan revolution speedNti for the intake air, a target fan revolution speed Nto for thehydraulic oil, and a target fan revolution speed Ntc for the coolant,are output from the PI control units 37,38,39 respectively. Limiters42,43,44 having saturation characteristics are provided so that eachlimiter 42,43,44 sets the upper and lower limits of each respectivesignal Nti,Nto,Ntc.

The target fan revolution speed Nti′ for the intake air, the target fanrevolution speed Nto′ for the hydraulic oil, and the target fanrevolution speed Ntc′ for the coolant that have passed through thelimiters 42,43,44 are input into an integrated target revolution speeddetermining unit 45, which determines a single integrated targetrevolution speed Ntt by performing calculation using these target fanrevolution speeds.

The integrated target revolution speed determining unit 45 may performthe aforementioned calculation by, for example, squaring each target fanrevolution speed Nti′,Nto′,Ntc′ of each respective cooling target fluid,summing up the squared values, and calculating the root of the sum. Theequation can be expressed as:Ntt={Σ(target fan revolution speed of each cooling target fluidn)²}^(1/2) orNtt={(Nti′)²+(Nto′)²+(Ntc′)²}^(1/2)

Upon being passed through a limiter 46, which has saturationcharacteristics so as to set the upper and lower limits of eachintegrated target revolution speed Ntt, the integrated target revolutionspeed Ntt resulting from the calculation becomes the final target fanrevolution speed Ntf.

As described above, the cooling system 30 consists of the intake aircooler 21, the oil cooler 22, the radiator 23, and the cooling fan 17shared by these three components. The controller 34 is programmed tocontrol the fan revolution speed of the cooling fan 17 of the coolingsystem 30 in order to achieve the target fan revolution speed Ntf sothat the detected temperature of each cooling target fluid, i.e. theintake air, the hydraulic oil, or the coolant, passing through thecooling system 30, i.e. the intake air cooler 21, the oil cooler 22, orthe radiator 23, is brought to the same level as each respective targettemperature when the flow rate of the cooling target fluid is high. Thecontroller 34 is also programmed to control the fan revolution speed ofthe cooling fan 17 to achieve a new target fan revolution speed Ntfnew,which is lower than the target fan revolution speed Ntf, should the flowrate of a cooling target fluid passing through the cooling system 30become lower.

Whether the flow rate of the cooling target fluid passing through thecooling system 30 is high or low is detected by system of the leveroperation detecting switches 36 lev. To be more specific, should thelever operation detecting switches 36 lev detect activation of eitherone or both of the operation levers 7L,7R, it is judged that eachcooling target fluid is passing through the cooling system 30 at a highflow rate. Should the operation levers 7L,7R be detected to be at theneutral position, it is judged that the cooling target fluid is passingthrough the cooling system 30 at a low flow rate.

When outputting a command for reducing the engine speed of the engine 11in cases where the levers are at the neutral position in order to bringthe engine speed to a level lower than in a case where either one orboth of the levers are being operated, the controller 34 calculates anew target fan revolution speed Ntfnew for the period during which thelevers are at the neutral position by multiplying the fan revolutionspeed Ntf at that time by the ratio (Ncoe/Nhie), in which Ncoerepresents the engine speed when the levers are at the neutral positionand Nhie represents the engine speed when at least one of the levers isoperated.

FIG. 4 shows in detail the aforementioned PI control unit 38 fortemperature of the hydraulic oil.

Referring to the drawing, a target temperature Tto and a detectedtemperature Tmo of the hydraulic oil are introduced to a comparator 51,which serves to calculate the difference between these temperatures. Asignal value is produced by multiplying a differential signal outputfrom the comparator 51 by a gain 52 and then setting the upper and lowerlimits of the resulting value by system of a limiter 53, which hassaturation characteristics. Another signal value is produced bymultiplying the aforementioned differential signal by a gain 54,performing integration of the resulting value by system of an integrator55, and then setting the upper and lower limits of the resulting valueby system of a limiter 53. By summing up the aforementioned signalvalues and an expected fan revolution speed Nef by system of an adder57, the aforementioned target fan revolution speed Nto for the hydraulicoil is determined.

When either one or both of the levers that serve to feed hydraulic oilto the hydraulic actuators, such as the boom hydraulic cylinders 5 bmc,are operated, the fan revolution speed of the oil cooler 22, whichserves to cool the return oil from the hydraulic actuators by system ofthe cooling fan 17, is controlled to achieve the target fan revolutionspeed Nto for the hydraulic oil so that the detected temperature Tmo ofthe hydraulic oil reaches the target temperature Tto. When the operationlevers are at the neutral position, supply of the hydraulic oil to thehydraulic actuators is at standstill, and the fan revolution speed ofthe cooling fan is controlled at a new target fan revolution speedNtonew, which is lower than the target fan revolution speed Nto.

When outputting a command for reducing the engine speed of the engine 11in cases where the levers are at the neutral position in order to bringthe engine speed to a level lower than in a case where either one orboth of the levers are being operated, the controller 34 calculates anew target fan revolution speed Ntonew for the period during which thelevers are at the neutral position by multiplying the current fanrevolution speed Nto for the hydraulic oil by the ratio of the enginespeed Ncoe to the engine speed Nhie, wherein Ncoe represents the enginespeed when the levers are at the neutral position and Nhie representsthe engine speed when at least one of the levers is operated.

In the same manner as above, the PI control unit 37 processes a targettemperature Tti and a detected temperature Tmi of the intake air todetermine a target fan revolution speed Nti for the intake air, and thePI control unit 39 processes a target temperature Ttc and a detectedtemperature Tmc of the coolant to determine a target fan revolutionspeed Ntc for the coolant. In addition, new target fan revolution speedsfor the intake air and the coolant are respectively determined.

To summarize, the fan revolution speed control method according to thepresent invention is a control method for calculating either an overalltarget revolution speed Ntf as shown in FIG. 3 or individual targetrevolution speeds, such as a target fan revolution speed Nto forhydraulic oil, as shown in FIG. 4, and reducing the calculated targetrevolution speed Ntf or each respective target revolution speedNti,Nto,Ntc to achieve the ratio Ncoe/Nhie, in which Ncoe represents theengine speed when the levers are at the neutral position and Nhierepresents the engine speed when at least one of the levers is operated.

The state where the operation levers 7L,7R are at the neutral positionand the engine speed is automatically reduced to the AEC revolutionspeed as a result of activation of AEC by system of the AEC switch 36aec is referred to as AEC status-ON. The state where the operationlevers 7L,7R are at the neutral position and the engine speed ismanually reduced to the one-touch low idling revolution speed as aresult of activation of one-touch low idling by system of the one-touchlow idling switch 8 is referred to as one-touch low idling status-ON.

The engine speed when the levers are at the neutral position, i.e. theengine speed Ncoe, is a command value output from the controller 34 asthe AEC revolution speed or the one-touch low idling revolution speed.The engine speed when at least one of the levers is in operation, i.e.the engine speed Nhie, is a high idling speed set by system of the axeldial 36 acc.

Next, the functions of the embodiment shown in the drawings areexplained hereunder.

Each PI control unit 37,38,39 includes a comparator 51 and othernecessary components. The temperatures of the cooling target fluids,i.e. the intake air, the hydraulic oil, and the coolant, arerespectively detected by the temperature sensors 28,28,29. As shown inFIGS. 3 and 4, based on data of these temperatures of the cooling targetfluids, a target fan revolution speed Ntf is obtained by system of thePI control units 37,38,39, the limiter 46, etc. The revolution speed ofthe cooling fan 17 is controlled to achieve the target fan revolutionspeed Ntf so that the detected temperature of each cooling target fluidreaches each respective target temperature.

To be more specific, information of the temperatures of the coolingtarget fluids detected by the temperature sensors 28,28,29 is constantlyor periodically fed back to calculation of fan revolution speeds so thatin cases where the detected temperature of any cooling target fluid fromamong the intake air, the hydraulic oil, and the coolant is higher thanits corresponding target temperature, the target fan revolution speedNtf is increased based on the difference in temperature so as to achievea better cooling effect. Thus, the fan revolution speed is controlledwithout using a revolution speed sensor.

Should the calorific value of a cooling target fluid increase, thecorresponding PI control unit 37,38,39 functions so that a higher fanrevolution speed is required for the temperature detected by thecorresponding temperature sensor 27,28,29 to reach the preset targettemperature.

For example, in cases where the target temperature and the detectedtemperature of the hydraulic oil are 60° C. and 61° C. respectively, thefan revolution speed of the cooling fan 17 begins to increase so thatthe detected temperature is brought down to 60° C. If the calorificvalue is very small, a minimal increase in the fan revolution speed issufficient for the detected temperature to return to 60° C. Should thecalorific value be great, a minimal increase in the fan revolution speedis not sufficient to stop the increase in the temperature of thehydraulic oil. As a result, the fan revolution speed, too, continues toincrease. When the fan revolution speed eventually reaches a sufficientlevel, the temperature of the hydraulic oil starts to decrease. Theincrease in the fan revolution speed stops when the temperature of thehydraulic oil reaches the target temperature.

Furthermore, even if the conditions of the target temperature and thecalorific value are the same, an increase in an ambient temperatureresults in a higher fan revolution speed of the cooling fan 17 asdescribed previously.

As explained above, a value to which the fan revolution speed iscontrolled is determined based on the calorific value and the ambienttemperature of each respective cooling target fluid. In other words, afeature of the control method according to the present embodiment liesin the absence of a map specifying each temperature and itscorresponding fan revolution speeds.

In cases where the integrated target revolution speed determining unit45 calculates an integrated target revolution speed Ntt based on theequation Ntt={Σ(target fan revolution speed of each cooling target fluidn)²}^(1/2), the integrated target revolution speed Ntt inevitablyincreases, when the fan revolution speed of any cooling target fluidincreases.

For example, when the target revolution speeds determined based on thetemperatures of the intake air, the coolant (cooling water), and thehydraulic oil are 300 rpm, 500 rpm, and 700 rpm respectively, theintegrated target revolution speed Ntt is 911 rpm. Under theseconditions, when the target revolution speed determined by the coolanttemperature increases from 500 rpm to 600 rpm, the integrated targetrevolution speed Ntt becomes 970 rpm.

Should the integrated target revolution speed be determined from theequation of Integrated target revolution speed=Maximum value (Fanrevolution speed of cooling target fluid n), the integrated targetrevolution speed is 700 rpm regardless of whether the target revolutionspeed determined by the coolant temperature is 500 rpm or 600 rpm. Inother words, the integrated target revolution speed remains unchangedregardless of the increasing calorific value of the entire system.

In cases where the hydraulic oil used in a vehicle, such as a hydraulicexcavator, is cool and does not require reduction of the temperature,the electro-hydraulic transducing valve 18 reduces the flow rate of thehydraulic oil discharged from the fan pump 13 in order to reduce the fanrevolution speed of the cooling fan 17. At that time, as the fan drivingpower of the engine 11 required by the fan pump 13 has decreased, theoutput of the main pump 12, which, too, is driven by the engine 11, canbe increased by an equivalent proportion. The method described abovethus enables the effective use of the output of the engine 11.Furthermore, the decrease in the fan revolution speed reduces noises ofthe cooling fan 17.

Next, the procedure of the fan revolution speed control method issequentially explained.

(1) The temperatures of the intake air, the hydraulic oil, and thecoolant (cooling water) of the engine 11 are respectively detected bythe temperature sensors 27,28,29.

(2) The difference between the target temperature of each cooling targetfluid, which is set in the controller 34 beforehand, and itscorresponding detected temperature detected by each respectivetemperature sensor 27,28,29 is calculated by the comparator 51 of thecorresponding PI control unit 37,38,39. Then, proportional integralcontrol is performed on each calculated difference by using the gains52,54 and the integrator 55.

(3) As a result of the PI control described above, the target fanrevolution speeds Nti,Nto,Ntc of the respective cooling target fluidsare determined. With these target fan revolution speeds input throughthe limiters 42,43,44, the target fan revolution speeds Nti′,Nto′,Ntc′are determined.

(4) The integrated target revolution speed determining unit 45determines a single integrated target revolution speed Ntt from theplurality of target fan revolution speeds Nti′,Nto′,Ntc′. To be morespecific, according to the present embodiment, the integrated targetrevolution speed is determined by calculation that uses the equationNtt={Σ(target fan revolution speed of each cooling target fluidn)²}^(1/2). As described later, however, the method of calculation isnot limited to this equation.

With the integrated target revolution speed Ntt input through thelimiter 46, the final target fan revolution speed Ntf is determined.

(5) By driving the electro-hydraulic transducing valve 18 so as toachieve the target fan revolution speed Ntf, the controller 34 controlsthe pump discharge rate of the fan pump 13, thereby controlling thenumber of revolutions of the fan motor 15. Thus, the fan revolutionspeed of the cooling fan 17 is controlled.

(6) In order for the detected temperatures of the cooling target fluidsto reach the respective target temperature, the process returns to (2)described above and continues feedback control.

(7) When at least one of the levers is being operated or in any othersituation where a large volume of a cooling target fluid or fluidspasses through the control system 30, which is provided with the coolingfan 17 for cooling the cooling target fluids, the fan revolution speedof the cooling fan 17 of the cooling system 30 is controlled to achievethe target fan revolution speed Ntf so that the detected temperatureTmi,Tmo,Tmc of each cooling target fluid reaches each respective targettemperature Tti,Tto,Ttc set beforehand. Should the flow rate of acooling target fluid or fluids passing through the control system 30 bereduced, such as when the levers are moved to the neutral position, thefan revolution speed of the cooling fan 17 is controlled to achieve thenew target fan revolution speed Ntfnew, which is lower than the targetfan revolution speed Ntf.

For example, when either one or both of the levers that serve to feedhydraulic oil to the hydraulic actuators are operated, the fanrevolution speed of the oil cooler 22, which serves to cool the returnoil from the hydraulic actuators by system of the cooling fan 17, iscontrolled to achieve the target fan revolution speed Nto for thehydraulic oil so that the detected temperature Tmo of the hydraulic oilin the hydraulic circuit reaches the target temperature Tto. When theoperation levers are at the neutral position, supply of the hydraulicoil to the hydraulic actuators is at standstill, and the fan revolutionspeed of the cooling fan is controlled at a new target fan revolutionspeed Ntonew, which is lower than the target fan revolution speed Nto.

As described above, when reducing the engine speed of the engine 11 incases where the levers are at the neutral position in order to bring theengine speed to a level lower than in a case where either one or both ofthe levers are being operated, a new target fan revolution speed Ntonewor Ntonew for the period during which the levers are at the neutralposition is calculated by multiplying the fan revolution speed Ntf orNto at that time by the ratio Ncoe/Nhie, wherein Ncoe represents theengine speed when the levers are at the neutral position and Nhierepresents the engine speed when at least one of the levers is operated.

As described above, the fan revolution speed control method according tothe invention does not call for detecting a fan revolution speed bysystem of a revolution speed sensor or the like to perform feedbackcontrol of the fan revolution speed. As it calls for feedback oftemperatures detected by the temperature sensors 27-29 for therespective cooling target fluids, the fan revolution speed in anabsolute value is not important.

As the value at which the fan revolution speed of each cooling targetfluid is regulated varies depending on the calorific value and theambient temperature of the cooling target fluid, target fan revolutionspeeds are respectively set for the cooling target fluids, and acalculating method for determining a single integrated target revolutionspeed based on these target fan revolution speeds is provided.

When the temperature of a cooling target fluid is low, the fanrevolution speed is reduced so that the power required to drive the fanis reduced. Therefore, the hydraulic output of the main pump can beincreased by the equivalent amount.

As control is performed to bring the detected temperatures of thecooling target fluids to reach the respective target temperatures, thetemperatures of the hydraulic oil and the cooling water rise faster inwinter. When the temperature of such a cooling target fluid as hydraulicoil changes, its viscosity, too, fluctuates. Therefore, the faster therise in the temperature of the cooling target fluid, the faster itsviscosity becomes stable. As a result, the fluctuation in the respondingtime caused by the difference in the viscosity of the cooling targetfluid, such as the hydraulic oil, is limited to a minimum, enabling theengine 11 to function at a more stable temperature.

The above description that states “control is performed so as to bringthe detected temperatures of the cooling target fluids to reach therespective target temperatures” includes cases where the cooling fan isbrought to a standstill or driven at a minimum fan revolution speed bycontrolling the discharge rate of the fan pump 13 to achieve 0 or aminimum amount by system of the electro-hydraulic transducing valve 18immediately after start-up of the engine in winter or under othersimilar conditions.

Should the flow rate of a cooling target fluid or fluids passing throughthe control system 30 be reduced, the fan revolution speed of thecooling fan 17 is controlled to achieve the new target fan revolutionspeed Ntfnew, which is lower than the target fan revolution speed Ntf.As this prevents rapid cooling of the cooling target fluid(s) flowing inthe cooling system 30 at a reduced flow rate and thereby suppressoccurrence of thermal strain in the cooling system, the durability ofthe cooling system 30 is improved.

For example, even when the hydraulic oil flowing in the oil cooler 22 ata reduced flow rate as a result of operating the levers to the neutralposition, reduction of the new target fan revolution speed Ntonew forthe period during which the levers are at the neutral position preventsthe hydraulic oil from being cooled rapidly so that occurrence ofthermal strain in the oil cooler 22 is suppressed, resulting in theimproved durability of the oil cooler 22.

At that time, when the levers are at the neutral position, the newtarget fan revolution speed Ntfnew or Ntonew for the period during whichthe levers are at the neutral position is calculated by reducing thetarget fan revolution speed Ntf or Nto to achieve the ratio Ncoe/Nhie,in which Ncoe represents the engine speed when the levers are at theneutral position and Nhie represents the engine speed when at least oneof the levers is operated. Therefore, the fan revolution speed isreduced to the optimal level without the problem of excessive reductionof the fan revolution speed.

The method of calculation for the integrated target revolution speeddetermining unit 45 to determine an integrated target revolution speedNtt is not limited to the one described above.

For example, the calculation may be performed by using a weightingfactor Wn (0≦Wn≦1, ΣWn=1) in the equation:Integrated target revolution speed Ntt=Σ{Wn×(target fan revolution speedof cooling target fluid n)}

The proportional integral control units that can be used for theinvention are not limited to the PI control units 37,38,39 describedabove and include proportional integral and differential control units(PID control units), which are widely used. Normal PID control units canbe used without a problem.

Referring to the flow chart shown in FIG. 1, an explanation is givenhereunder of the fan revolution speed control method that calls forreducing the fan revolution speed so as to suppress occurrence ofthermal strain in the oil cooler when the levers are at the neutralposition. In FIG. 1, numerals enclosed with circles represent stepnumbers.

The controller 34 regards the state where the AEC is in operation as AECstatus-ON and the state where engine is at the one-touch low idlingrevolution speed as a result of operation of the one-touch low idlingswitch 8 as one-touch low idling status-ON. The controller 34 determineswhether the AEC status has become ON as a result of operating the leversto the neutral position (Step 1). The controller 34 also determineswhether the one-touch low idling status has become ON as a result of theoperating the levers to the neutral position (Step 2). Should neither bethe case, in other words when at least one of the operation levers 7L,7Rhas been operated, the controller 34 commands the electro-hydraulictransducing valve 18 the fan revolution speed Ntf (Step 3).

Upon ascertaining whether the status is AEC status-ON or one-touch lowidling status-ON, the controller 34 initiates fan revolution speedreduction control, which calls for calculating a new target fanrevolution speed Ntfnew for the period during which the levers are atthe neutral position by multiplying the fan revolution speed Ntf at thattime by the ratio of the engine speed Ncoe to the high-idling enginespeed Nhie, in which the engine speed Ncoe serves as the target speedwhen the levers are at the neutral position and the high-idling enginespeed Nhie is the engine speed when at least one of the levers isoperated. The controller 34 then outputs the calculated target fanrevolution speed Ntfnew as a command to the electro-hydraulictransducing valve 18 (Step 4).

When the levers are at the neutral position, the high-idling enginespeed Nhie set by system of the axel dial 36 acc is reduced to theengine speed Ncoe, which is the engine speed for the period during whichthe status is AEC status-ON or one-touch low idling status-ON. In Step 4described above, the fan revolution speed Ntf is reduced to the newtarget fan revolution speed Ntfnew so as to achieve the ratio of theengine speed Ncoe to the high-idling engine speed Nhie.

Reducing the target fan revolution speed Ntf for the period during whichthe levers are at the neutral position to the new target fan revolutionspeed Ntfnew in the manner described above prevents rapid cooling of thehydraulic oil in the oil cooler 22, thereby suppressing occurrence ofthermal strain in the oil cooler 22.

Reducing the fan revolution speed Ntf so as to achieve the ratioNcoe/Nhie of the engine speed, wherein Ncoe represents the engine speedfor the period during which the status is AEC status-ON or one-touch lowidling status-ON prevents excessive reduction of the fan revolutionspeed and enables the reduction of the fan revolution speed to theoptimal level.

The results offered by the fan revolution speed control method describedabove include the following.

Thermal strain does not occur in the oil cooler 22 when the levers areat the neutral position. Therefore, the durability of the oil cooler 22is improved.

As the fan revolution speed is reduced, the amount of fuel consumed dueto revolution of the cooling fan is reduced, resulting in better fuelefficiency.

As the fan revolution speed is lower when the levers are at the neutralposition, noise produced by the revolution of the fan is reduced,alleviating discomfort for an operator.

As the fan revolution speed is lower when the levers are at the neutralposition, vibration produced by the revolution of the fan is reduced,resulting in the improved durability of the components.

ACTUAL EXAMPLE 1

Next, the present invention is explained using specific values,referring to a case where the invention is applied to a large hydraulicexcavator, for example an 85 t-class hydraulic excavator. When AEC is inthe second stage with the levers of the hydraulic excavator at theneutral position, the engine speed commanded by the controller 34 is1300 rpm, and the high-idling engine speed is 1980 rpm. Therefore, thenew target fan revolution speed Ntfnew is calculated by reducing thetarget fan revolution speed Ntf that corresponds to the temperature atthat time to achieve the ratio of 1300/1980. The fan revolution speed iscontrolled to achieve the new target fan revolution speed Ntfnew.

In cases where AEC is in the first stage when the levers are at theneutral position, the engine speed commanded by the controller 34 is 100rpm lower than the value set by the axle dial 36 acc. The new target fanrevolution speed Ntfnew is calculated by reducing the target fanrevolution speed Ntf that corresponds to the temperature at that time toachieve the ratio of the aforementioned commanded engine speed to thehigh-idling engine speed. The fan revolution speed is controlled inaccordance with the new target fan revolution speed Ntfnew.

When the engine is in the one-touch low idling state, the high-idlingengine speed of 1980 rpm is reduced to the low-idling engine speed of1100 rpm. Therefore, the new target fan revolution speed Ntfnew iscalculated by reducing the target fan revolution speed Ntf thatcorresponds to the temperature at that time to achieve the ratio of1100/1980. The fan revolution speed is controlled in accordance with thenew target fan revolution speed Ntfnew.

POSSIBLE INDUSTRIAL APPLICATION

The present invention is applicable to not only a construction machine,such as a hydraulic excavator, but also any other work machine thatrequires control of the fan revolution speed of its cooling fan.

1. A fan revolution speed control method comprising steps of: detectinga temperature of a cooling target fluid, and controlling the fanrevolution speed of a cooling fan of a cooling system for cooling saidcooling target fluid so that: when the flow rate of said cooling targetfluid passing through said cooling system is high, the fan revolutionspeed of said cooling fan is controlled to achieve a target fanrevolution speed in order to bring the detected temperature to the samelevel as a preset target temperature, and that when the flow rate ofsaid cooling target fluid becomes lower, the fan revolution speed of thecooling fan is controlled to achieve a new target fan revolution speedthat is lower than said target fan revolution speed.
 2. A fan revolutionspeed control method comprising steps of: detecting a temperature ofhydraulic oil in a hydraulic circuit, and controlling the fan revolutionspeed of a cooling fan of an oil cooler that serves to cool the returnoil from a hydraulic actuator so that: when a lever for feedinghydraulic oil to said hydraulic actuator is being operated, the fanrevolution speed of said cooling fan is controlled to achieve a targetfan revolution speed in order to bring the detected temperature to thesame level as a preset target temperature, and that when the lever is ata neutral position, during which period supply of the hydraulic oil tosaid hydraulic actuator is at standstill, the fan revolution speed ofsaid cooling fan is brought to a new target fan revolution speed that islower than said target fan revolution speed.
 3. A fan revolution speedcontrol method as claimed in claim 2, wherein: when reducing the enginespeed of a pump driving engine in the hydraulic circuit for the periodduring which said lever is at said neutral position to a level lowerthan that for the period during which said lever is being operated, saidnew target fan revolution speed for the period during which said leveris at the neutral position is calculated by multiplying the fanrevolution speed at that time by the ratio of the engine speed for theperiod during which said lever is at the neutral position to the enginespeed for the period during which said lever is being operated.